The present invention relates to an electrically conductive resin composition suitable for use as a material to form the cylindrical base of the photosensitive drum in electrophotographic machines such as copying machines, facsimiles, and printers. The present invention relates also to a photosensitive drum whose cylindrical base is made with the electrically conductive resin composition.
Copying machines, facsimiles, and printers employ the electrostatic recording process. The process for printing consists of uniformly charging the surface of a photosensitive drum, projecting an image onto the charged surface through an optical system so that charge disappears from the exposed part, thereby forming a latent image thereon, supplying the latent image with a toner, thereby forming a toner image due to electrostatic attraction between them, and transferring the toner image to a recording medium such as paper, OHP, and photographic paper.
The above-mentioned electrostatic recording process usually employs a photosensitive drum constructed as shown in FIG. 1.
Specifically, it consists of a cylindrical base 1 having good electrical conductivity, two flanges 2a and 2b fitted into both ends of the cylindrical base 1, and a photosensitive layer 3 formed on the peripheral surface of the cylindrical base 1. As shown in FIG. 1, the photosensitive drum is usually supported by two axes 4 and 4 fixed to the main body 10 of the electrophotographic apparatus and the axes are inserted into the holes 5 and 5 formed in the flanges 2a and 2b, so that the photosensitive drum turns freely. On the periphery of one flange 2b is formed a gear 6 which engages with a gear 7 connected to a drive motor. The cylindrical base 1 thus constituted is allowed to rotate.
The cylindrical base 1 mentioned above is conventionally made with aluminum alloy because of its light weight, good machinability, and high electrical conductivity.
Unfortunately, the cylindrical base of aluminum alloy needs high-precision machining if it is to meet stringent requirements for dimensions and surface roughness. It also needs machining for the holes into which the flanges 2a and 2b are fitted. Moreover, it may need surface treatment to prevent surface oxidation. These added steps lead to a high production cost. Therefore, aluminum alloy is not necessarily a satisfactory raw material for the cylindrical base to constitute the photosensitive drum.
There has been proposed an idea of making the cylindrical base 1 from a resin composition composed mainly of polyphenylene sulfide (PPS) resin by injection molding. The molding process is comparatively easy and the resulting cylindrical base is light in weight and superior in chemical and heat resistance. In addition, the cylindrical base 1 can be molded integrally with either of the flanges 2a and 2b from the same resin composition.
When the above-mentioned PPS-based resin composition is made into the cylindrical base 1 for the photosensitive drum, it is usually incorporated with carbon black in an amount more than 20% by weight so that it is given electrical conductivity. Unfortunately, any PPS resin composition with such a high content of carbon black is very brittle and hence it is incorporated with a reinforcement such as glass fiber so that the resulting cylindrical base has a required strength.
The disadvantage of the PPS resin composition incorporated with carbon black and glass fiber is extremely poor in flowability in the molten state. Thus the resulting cylindrical base is poor in surface smoothness because the finished surface of the mold is not completely transferred at the time of injection molding. This poses a serious problem in the subsequent steps of applying a photosensitive material to the surface, thereby forming a photosensitive layer.